The International Classification of Sleep Disorders distinguishes more than 80 different disorders, which can be effectively treated. Problems with falling asleep or daytime sleepiness affect approximately 35 to 40% of the U.S. adult population annually and are a significant cause of morbidity and mortality. A disturbed sleep diminishes the recreation it provides to the sleeper. If bad sleep quality prevails over extended periods of time, it can lead to a bad general health condition, limited energy and stress resistance. Difficulties in falling asleep affect 6%-9% of the general population. However, especially in elderly patients the prevalence is much higher. A study investigating people aged 66-97 found difficulties initiating sleep in 26.7% of the male test subjects and in 44.1% of the female test subjects.
People with problems staying asleep report that they can fall asleep fairly well, but wake up a couple of hours later and cannot get back to sleep. Reasons can be manifold. If somebody wakes up and his thoughts keep spinning around his worries, what he experienced throughout the day and his plans for the next day etc., he will have difficulties to clear his mind and relax sufficiently in order to fall asleep again.
WO2007105127 A1 discloses a system for inducing a subject to fall to sleep, comprising a light pattern generator for generating a time varying light pattern in view of the subject. Further, the system comprises a breathing rate measuring unit for measuring a breathing frequency of the subject. In addition, the system comprises a control unit connected to the breathing rate measuring unit and the light pattern generator, for controlling the light pattern generator, such that the generated light pattern has a pattern frequency substantially between the measured breathing frequency and a pre-selected desired frequency. However, such a system may not induce sleep in the subject satisfactorily.